package suanfa;

import javax.swing.tree.TreeNode;
import java.util.*;

public class zigzagLevelOrder {
      public class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode() {}
      TreeNode(int val) { this.val = val; }
      TreeNode(int val, TreeNode left, TreeNode right) {
          this.val = val;
          this.left = left;
          this.right = right;
      }
  }
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> ret=new ArrayList<>();
        if(root==null) return ret;
        Queue<TreeNode> q=new LinkedList<>();
        q.add(root);
        int level=1;
        while(!q.isEmpty()){
            int sz=q.size();
            List<Integer> tmp=new ArrayList<>();
            for(int i=0;i<sz;i++){
                TreeNode t=q.poll();
                tmp.add(t.val);
                if(t.left!=null) q.add(t.left);
                if(t.right!=null) q.add(t.right);
            }
            //判断是否逆序
            if(level%2==0) Collections.reverse(tmp);
            ret.add(tmp);
            level++;
        }
        return ret;
    }
}
